There is known a wire coating stripping apparatus (hereinafter may be referred to as a wire stripper) configured such that stripping blades are fed into a coating of an electric wire and the stripping blades are moved relatively against the electric wire, thereby to strip (strip away) a part of the coating.
When the wire coating is stripped by such a wire stripper, it is necessary to feed the stripping blades into the wire coating as deeply as possible to make a cutting edge of the wire coating more precise and sharp. The wire core may, however, be subject to be scratched or a part of it may be cut off if the blade comes in contact with the wire core to result in rejection of the electric wire concerned.
Since absolute safety is demanded especially for the electric wire for automotive or aircraft industries, even an electric wire having the slightest scratches on its core is rejected for the reason that it may be damaged and lead to serious accidents if used for movable parts or in any position subject to vibrations because of stress concentration on the scratches.
A function to detect any contact between the wire core and the stripping blade is, therefore, deemed as indispensable for the wire stripper so that a number of automatic wire strippers developed in recent years are provided with the said function of contact detection. Most of them, however, use a method to detect any contact between the wire core and the blade through detection of electric conduction between electrodes which are allocated to them, respectively.
As an example, a wire core scratch detector according to the patent document 1 (Japanese Patent Application Laying Open (KOKAI) No. 7-87643) referred to later is described in the following while taking FIG. 10 as the basis.
According to this heretofore known technique, an electric wire 63 is led through a wire guide 84 and fastened by a wire gripper 85. A cassette blade 86 is then put into operation to make an incision on an insulating coating 71 of a core 70 of the electric wire 63 by means of incision making cutters 87 and to cut the electric wire 63 by means of cutting blades 82 so as to strip the coating by simultaneously pulling it axially by means of a wire gripper 85.
When the incision making cutters 87 in the cassette blade 86 come now in contact with the wire core 70 in the phase of incision to the coating 71, an alternating current flows through it by way of a capacitance arising between the electric wire 63 and the wire gripper 85, a detector 88 and an AC power supply 89 in the said order. A voltage corresponding to this current is detected by the detector 88 to confirm the contact of the incision making cutter 87 with the wire core 70.
It is extremely difficult for the method of detecting core scratches according to the patent document 1 as shown in FIG. 10 to ensure a point to attach a corresponding mechanism if the electric wire to be finished is of short lengths. The said detection method is inappropriate also from the safety point of view in case of manual stripping operation by use of a desktop wire stripper.
In view of this, the present applicants have already proposed a wire stripper (hereinafter referred to as a wire stripper of our prior patented invention) as in the following patent document 2 (Japanese Patent No. 4883821) disclosing an earlier filed patent application owned by the applicants, which uses a cutter (stripping blades) as a detection sensor to detect an impedance (including resistance, inductance, and capacitance) of a wire core of an electric wire, and thereby to be able to detect a wire core scratch with high precision under the same conditions for the electric wire cut to any length, no matter how short or how long it is.
According to the wire stripper of the prior patented invention, as illustrated in FIG. 11, an electric signal from an electric signal generator circuit (signal generating circuit) 75 passes through a current limiting circuit 76 to a conductor 73 and then given to stripping blades 27 and 27. The electric signal further passes through a filter circuit 77 for removing noise and the like, then through a signal amplifier circuit 78 for monitoring a minute change at the moment of a contact of the stripping blades 27 and 27 with the wire core 70, and then transmitted to a signal analyzer circuit 74. A logic circuit for determination (signal determination circuit) 80 receives a signal from the signal analyzer circuit 74 and a preset determination time for wire coating stripping operation from a control circuit 79 to finally determine whether or not there is a contact between the stripping blades 27 and 27 and the wire core 70. If a determination is made that there is a harmful contact therebetween, an error (Err) is displayed on a display window 21 with a display device.
The electric signal can be sampled in cycles e.g. on the microsecond time scale. When the stripping blades 27 contact the wire core 70 of electric wire W (63), a pulse output is generated according to the position of the stripping blades at a time when the coating 71 is stripped. The pulse is detected by the signal analyzer circuit 74 as a change in impedance caused by addition of the impedance of the wire core 70.
In this manner, when a detection is made whether or not the stripping blades contact the core wire, the contact position and temporal elements can be arbitrarily set to monitor the temporal elements such as the contact time between the stripping blades 27 and 27 and the core wire 70, and the position thereof during the period of time immediately from the start of the stripping operation to the end thereof, the function of which can be used to determine that even if the stripping blades contact the core wire, the wire is not considered as defective depending on the degree and the position thereof so as to prevent unwanted operation stop when the wire stripper is adopted in an automatic machine and the like.